1. Field of the Invention
The present invention relates to a sound absorbing structure excellent in durability, weather resistance and recycling easiness.
2. Description of the Related Art
Sound-proof walls for preventing noise are provided for an expressway and a railroad. In general, the sound-proof wall is constituted by sound absorbing panels each having a panel-shape structure which accommodates inorganic fibers, such as glass wool or rock wool.
The sound absorbing panel constituted by the inorganic fibers suffers from the following problems:
(1) Glass wool and the like have a problem of unsatisfactory water draining performance. When moisture content is absorbed, the sound absorbing performance deteriorates. Therefore, complicated maintenance of the performance must be performed.
(2) Glass wool and the like encounter xe2x80x9cfatiguexe2x80x9d owing to use for a long time. Thus, the sound absorbing performance and the strength deteriorate.
(3) When the period of durability has elapsed, recycling requires a great cost. In general, a waste disposal process of the glass wool or the like must be performed as the industrial waste. In the foregoing case, recycling of rock wool does not require a high cost which is required for the glass wool. However, the cost is not satisfactorily low.
(4) When the glass wool or the like is exposed to air flows, flying and flotation of the fibers easily occurs. Thus, the sound absorbing performance deteriorates.
(5) In an environment, such as a location for manufacturing foods or chemicals, which requires a high degree of cleanness, flying and flotation of fibers cause a problem to arise. Therefore, the foregoing material cannot easily be employed.
(6) When the foregoing material is handled, there arises problems of aspiration and prickling of the fibers.
(7) The inorganic fibers deteriorate and become brittle owing to exposure to ultraviolet rays for a long time. Therefore, a countermeasure against the foregoing problem must be taken when the inorganic fibers is used outdoors.
(8) To solve the problems (1) and (4) to (7), a means for covering the inorganic fiber material with PVF films or the like is employed. In this case, there arises a problem in that the sound absorbing performance deteriorates and the films are broken.
Since a large quantity of the sound absorbing panels are used especially in a an expressway and railroad, the foregoing problem (3) is a critical problem which must be solved also from a viewpoint of the environment protection.
As a sound absorbing material which does not raise the problems experienced with the inorganic fibers, for example, a structure formed into a plate-like shape is known which is obtained by pressurizing and compressing aluminum fibers. Also a sound absorbing member is known which is obtained by foaming sintered aluminum particles or an aluminum material.
The sound absorbing member made of the foregoing metal material encounters a problem of inferior sound absorbing performance to that of the sound absorbing member made of the inorganic fibers, such as glass wool or the rock wool.
The foregoing sound absorbing members absorb sound by converting a part of acoustic energy into heat energy caused from friction of molecules in the air against the fibers and the particles when the molecules in the air pass through the gaps of the fibers or the particles.
The effect of absorbing sound using the foregoing sound absorbing member can be improved such that further bass range sound can be absorbed when the thickness of the rear air layer is enlarged. In usual, the size (in particular, the thickness) of the sound absorbing panel is, however, limited. Therefore, satisfactory sound absorbing performance cannot easily be realized in a frequency range not higher than 500 Hz. In particular, the sound absorbing member of a type constituted by the metal material demonstrates a propensity to have the foregoing characteristic.
As one of means for absorbing sound, a method is known which uses the following resonant structure. That is, the method uses the Helmholtz resonant structure as the basic principle thereof. As distinct from the sound absorbing member represented by fibers, frictional loss of movement of air occurring when the resonant structure called a Helmholtz resonator causes loss of the acoustic energy in the vicinity of the resonant frequency range to be produced. Thus, sound absorbing effect can be obtained.
As a representative sound absorbing structure using the Helmholtz resonator as the principle thereof, a structure is exemplified in which the surface of the wall is constituted by plates each having a multiplicity of openings or slits. Moreover, an air layer is formed in the rear portion of the sound absorbing structure. In this specification, a structure using the Helmholtz resonance as the basic principle for absorbing sound is hereinafter called a resonant sound absorbing structure.
A usual resonant sound absorbing structure encounters a problem in that the sound absorbing performance can be obtained only in a range in the vicinity of a specific resonant frequency. However, the foregoing structure has a characteristic that sound absorption is permitted in a bass range which cannot easily be realized when the sound absorbing member is employed.
In Japanese Examined Utility Model Publication Hei. 5-2646, a structure has been disclosed which includes sound absorbing members each incorporating aluminum fibers to serve as the sound absorbing materials, wherein the sound absorbing members are disposed in a state where air layers are formed such that the sound absorbing members are disposed apart from one another. Thus, sound absorption owing to the sound absorbing members and sound absorption owing to the resonant structure (resonant spaces) constituted by the gaps of the sound absorbing members and the rear air layers can simultaneously be performed.
The foregoing structure incorporating the aluminum fibers is able to solve the problems experienced with the structure incorporating the inorganic fiber sound absorbing member. Moreover, the sound absorbing performance in the bass range is attempted to be improved by also employing the resonant sound absorbing structure. The disclosed structure, however, has a problem in that a complicated structure is required and installation of the structure cannot be easily performed.
In general, the sound absorbing member constituted by forming aluminum fibers into a plate-like shape suffers from unsatisfactory strength. Therefore, a large size structure cannot be realized. Hence it follows that a satisfactorily large sound absorbing member cannot be obtained by the disclosed structure. Thus, there arises a problem in that a multiplicity of sound absorbing members must be joined and, therefore, the cost required to install the structure becomes high.
Moreover, the sound absorbing members must individually be disposed at positions apart from one another for predetermined distances. In addition, the air layers must be formed in a state where the sound absorbing members have been disposed. As a result, the overall structure is enlarged and complicated excessively. It leads to a fact that the cost required to install the structure becomes high.
The foregoing structure does not permit a sufficiently long length of the neck in each gap (the dimension in the direction of the depth of the inlet/outlet portion of the resonant structure). Therefore, when a resonant sound absorbing structure which is effective up to a furthermore bass range is required, the capacity of the resonant space must be enlarged. Hence it follows that the overall structure is enlarged excessively. Thus, the portion for which the sound absorbing structure can be provided is limited. When the space for installing the sound absorption structure required for a road or a railway is usually limited. Therefore, thick air layers cannot easily be provided. As a result, the foregoing structure cannot be easily put into practical use.
Therefore, development of a sound absorbing structure having a small thickness and free from limitation of the portion for installation is required.
In view of the foregoing, an object of the present invention is to provide a sound absorbing structure incorporating a metal material serving as a sound absorbing member and satisfying the following requirements.
(1) Both of the sound absorbing effect obtainable from the sound absorbing member and the sound absorbing effect obtainable from the slit resonant sound absorbing structure are used to improve the sound absorbing performance in a bass range.
(2) A high sound absorbing performance can be realized in a wide frequency range.
(3) A structure is free from useless portions and simple, and the weight can be reduced.
(4) The installation of the structure can easily be performed with a low cost.
(5) The thickness of the structure can be reduced. When a sound absorbing panel structure is employed, an integrated panel structure can be realized. Easiness in handling is required, and the portion for which the structure is provided is not limited.
(6) Recycling can easily be performed.
(7) Satisfactory weather resistance can be realized.
A first aspect of the present invention has a structure comprising: a surface plate constituted by a plate-like or planar sound absorbing member; a rear air layer; and a slit resonant sound-absorbing structure which are formed in the rear of the sound absorbing member. The plate-like or planar sound absorbing member serving as the surface plate, the rear air layer and the slit resonant sound absorbing structure are unified into one structure.
A second aspect of the present invention has a structure comprising: a surface plate constituted by a sound absorbing member obtained by compression molding metal fibers into a plate-like shape; a rear air layer; and a slit resonant sound absorbing structure which are formed in the rear of the sound absorbing member. A third aspect of the present invention has a structure that each of five sides of the sound absorbing member except for the surface plate has a hollow box-shape structure constituted by a plate-like member made of a non-ventilation material.
A fourth aspect of the present invention has a structure that a plurality of elongated members for constituting the air layer are disposed below the sound absorbing member at positions apart from one another for a predetermined distances, and the slit resonant sound absorbing structure is constituted by using the gaps between adjacent elongated members. A fifth aspect of the present invention has a structure that the sound absorbing member is supported by a plurality of elongated members disposed in the structure at positions apart from one another for a predetermined distance, each of the elongated members has a concave cross sectional shape which has an internal space in which a rear air layer of the sound absorbing member is formed and which is made of a non-ventilation material, and a slit resonant sound absorbing structure is formed in a gap between the elongated members and the bottom surface of the structure and a gap between adjacent elongated members. The bottom surface of the structure means a bottom plate when the structure is the sound absorbing panel. When the structure is integrally joined to the wall surface of a building structure, the bottom surface means the surface of the wall.
A sixth aspect of the present invention has a structure that one or more types of rear air layer and slit resonant sound absorbing structures are formed in each of the internal spaces (a recessed internal space) of the elongated members. When one or more types of individual elongated members are disposed in the internal space of the elongated members, the rear air layer and the slit resonant sound absorbing structure having a new shape and dimensions are formed.
A seventh aspect of the present invention has a structure that a plurality of the widths of the rear air layer or/and the widths (the slit widths) of a slit opening of the slit resonant sound absorbing structure are set. The widths of the grooves and the slits are not made to be constant. The widths of the grooves and the slits are varied widely. The slit widths may be changed in accordance with a predetermined rule, or the change may be realized without any rule. In addition, the widths of the grooves and slits formed in the internal spaces of the elongated members are changed.
An eighth aspect of the present invention has a structure that a sound absorbing characteristic of the rear air layer and the sound absorbing characteristic of the slit resonant sound absorbing structure are compensated each other so as to obtain the sound absorbing performance in a wide frequency range. When the sound absorbing performance of each of the rear air layer and the slit resonant sound absorbing structure are graphed, trough portions in each of which the sound absorption coefficient is low are compensated each other. Thus, the trough portions are eliminated to eradicate the frequency range which cannot be absorbed.
The ninth aspect of the invention has a structure that the concave cross sectional shape of the elongated member is formed into anyone of a U-shape facing side, a U-shape, a V-shape, a semi-circular shape, a triangular shape, a trapezoidal shape or their mixture. The tenth aspect of the invention has a structure that the structure is reinforced by the elongated members. The eleventh aspect of the invention has the structure that the resonant sound absorbing structure is constituted by using the wall surfaces of a building structure.
According to the first and second aspects of the present invention, the plate-like or planar sound absorbing member, and in particular a sound absorbing member obtained by compression molding metal fibers is employed as the surface plate of the structure. Moreover, the rear air layer of the sound absorbing member and the slit resonant sound absorbing structure are formed in the structure. Thus, high sound absorbing performance and, in particular, satisfactory sound absorbing performance to a low frequency can be obtained. Moreover, an integrated-type sound absorbing panel exhibiting satisfactory handling easiness can be obtained.
When a sound wave in a specific resonant frequency range (which is somewhat broad range) has been made incident on the slit resonant sound absorbing structure, a resonance phenomenon occurs. Thus, air blocks are fiercely introduced/discharged with respect to the slit portions. At this time, the acoustic resistance of the slit portion causes the kinetic energy of the movement of air to be lost. Thus, the acoustic energy is lost.
Thus, sound absorption in the specific frequency range can be realized. In the present invention, the sound absorbing members constituted by the metal fibers are disposed in the openings of the slits. Therefore, the resistance which is exerted on the air which is introduced/discharged with respect to the slits when resonance occurs is raised. Therefore, the sound absorption owing to the foregoing mechanism is performed at a high efficiency. Since thin plate-like sound absorbing members are employed, spaces required for the rear air layer and the slit resonant sound absorbing structure can effectively be created in a limited space.
The third aspect of the invention incorporates the hollow box-shape structure having the bottom plate and the right and left side plates except for the surface plate of the sound absorbing member are made of non-ventilation material materials. Therefore, a sound absorbing panel having a simple structure, high strength and easy handling characteristic can be obtained. Moreover, the air inlet/outlet openings of the slit resonant sound absorbing structure are limited to only the slit portions. Therefore, the sound absorbing effect can be improved.
The fourth, fifth and ninth aspects of the invention enabled the rear air layer of the sound absorbing member and the slit resonant sound absorbing structure to be obtained with a simple structure. Moreover, a structure with which the sound absorbing member can be reliably supported can be obtained. In addition, the elongated members enable the depths (for example, the dimension in the direction of the depth of a gap 11 shown in FIG. 2) of the necks of the slit resonant sound absorbing structure to be maintained. Thus, a limited resonant space can be used to obtain a resonant sound absorbing structure which is effective to a bass range.
The sixth aspect of the invention enables the rear air layers and the slit resonant sound absorbing structures having different shape and dimensions to be obtained in the sound absorbing structure. The seventh aspect of the invention enables two or more types of the rear air layers and slit resonant sound absorbing structures having different groove widths and slit widths to be obtained.
The tenth aspect of the invention enables a sound absorbing panel having a robust structure and exhibiting excellent handling characteristic to be obtained. That is, the slit resonant sound absorbing structure can be formed by the elongated members, and the sound absorbing members can reliably be supported. Moreover, the elongated members serve as beams so that reinforced sound absorbing panels are obtained. The eleventh aspect of the invention uses the wall surfaces of a building structure as a substitute for the bottom plates of the sound absorbing panels so that a low-cost sound absorbing structure is obtained which effectively uses the space.